Systems and methods to determine hr, rr and classify cardiac rhythms based on atrial iegm and atrial pressure signals

ABSTRACT

Systems, devices and methods described herein can be used to monitor and treat cardiovascular disease, and more specifically, can be used to determine heart rate (HR), determine respiration rate (RR) and classify cardiac rhythms based on atrial intracardiac electrogram (IEGM) and atrial pressure (AP) signals. The atrial IEGM and AP signals are subject to spectrum transforms to obtain an atrial IEGM frequency spectrum and an AP frequency spectrum. Based on peaks in the atrial IEGM and AP frequency spectrums measures of HR and RR are determined, and arrhythmias are detected and/or arrhythmia discrimination is performed.

FIELD OF THE INVENTION

Embodiments of the present invention generally relate to systems,devices and methods that can be used to monitor and treat cardiovasculardisease, and more specifically, can be used to determine heart rate(HR), determine respiration rate (RR) and classify cardiac rhythms basedon atrial intracardiac electrogram (IEGM) and atrial pressure (AP)signals.

BACKGROUND

The optimum management of patients with chronic diseases requires thattherapy be adjusted in response to changes in the patient's condition.Ideally, these changes are measured by daily patient self-monitoringprior to the development of symptoms. Self-monitoring andself-administration of therapy forms a closed therapeutic loop, creatinga dynamic management system for maintaining homeostasis. Such a systemcan, in the short term, benefit day-to-day symptoms and quality-of-life,and in the long term, prevent progressive deterioration andcomplications.

There are tens of millions of people in the U.S. with risk factors fordeveloping chronic cardiovascular diseases, including high bloodpressure, diabetes, coronary artery disease, valvular heart disease,congenital heart disease, cardiomyopathy, and other disorders.Additional millions of patients have already suffered quantifiablestructural heart damage but are presently asymptomatic. Still yet, thereare millions of patients with symptoms relating to underlying heartdamage defining a clinical condition known as congestive heart failure(CHF). Although survival rates have improved, the mortality associatedwith CHF remains worse than many common cancers. The number of CHFpatients is expected to grow as the population ages and more people withdamaged hearts are surviving.

CHF is a condition in which a patient's heart works less efficientlythan it should, and a condition in which the heart fails to supply thebody sufficiently with the oxygen-rich blood it requires, either duringexercise or at rest. To compensate for this condition and to maintainblood flow (cardiac output), the body retains sodium and water such thatthere is a build-up of fluid hydrostatic pressure in the pulmonary bloodvessels that drain the lungs. As this hydrostatic pressure overwhelmsoncotic pressure and lymph flow, fluid drains from the pulmonary veinsinto the pulmonary interstitial spaces, and eventually into the alveolarair spaces. This complication of CHF is called pulmonary edema, whichcan cause shortness of breath, hypoxemia, acidosis, respiratory arrest,and death. Although CHF is a chronic condition, the disease oftenrequires acute hospital care. Patients are commonly admitted for acutepulmonary congestion accompanied by serious or severe shortness ofbreath. Acute care for CHF accounts for the use of more hospital daysthan any other cardiac diagnosis, and consumes billions of dollars inthe United States annually.

Not all CHF patients suffer debilitating symptoms immediately. Some maylive actively for years. Yet, with few exceptions, the disease isrelentlessly progressive. As CHF progresses, it tends to becomeincreasingly difficult to manage. Even the compensatory responses ittriggers in the body may themselves eventually complicate the clinicalprognosis. For example, when the heart attempts to compensate forreduced cardiac output, ventricular muscle mass increases due toincreased work that ventricles must perform with each heartbeat. Thisplaces a still higher demand on the heart's oxygen supply. If the oxygensupply falls short of the growing demand, as it often does, furtherinjury to the heart may result. The additional muscle mass may alsostiffen the heart walls, which further reduces cardiac output.

Current standard treatment for CHF is typically centered around medicaltreatment using ACE inhibitors, diuretics, and digitalis. It has alsobeen demonstrated that aerobic exercise may improve exercise tolerance,improve quality of life, and decrease symptoms. Cardiac surgery has alsobeen performed on a small percentage of patients with particularetiologies. Although advances in pharmacological therapy havesignificantly improved the survival rate and quality of life ofpatients, some CHF patients are refractory to drug therapy, have limitedexercise tolerance, and a poor prognosis. In recent years, cardiacpacing, in particular Cardiac Resynchronization Therapy (CRT), hasemerged as an effective treatment for many patients with drug-refractoryCHF.

CHF patients require close medical management to reduce morbidity andmortality. Because the disease status evolves over time, frequentphysician follow-up examinations are often necessary. At follow-up, thephysician may make adjustments to the drug regimen in order to optimizetherapy. This conventional approach of periodic follow-up may be lesssatisfactory for CHF, in which acute, life-threatening exacerbations candevelop between physician follow-up examinations. It is well known amongclinicians that if a developing exacerbation is recognized early, it canbe more easily and inexpensively terminated, typically with a modestincrease in oral diuretic. However, if it develops beyond the initialphase, an acute CHF exacerbation becomes difficult to control andterminate. Hospitalization in an intensive care unit is often required.It is during an acute exacerbation of CHF that many patients succumb tothe disease. Early identification may also allow for pacing therapy froman implanted pulse generator. In view of the above, it would bebeneficial if a patient's CHF condition could be chronically monitored.

In a normal heart, cells of the sinoatrial node (SA node) spontaneouslydepolarize and thereby initiate an action potential. This actionpotential propagates rapidly through the atria (which contract), slowlythrough the atrioventricular node (AV node), the atrioventricular bundle(AV bundle or His bundle) and then to the ventricles, resulting in aventricular contraction. This sequence of events is known as sinusrhythm (SR). Thus, in a normal heart, ventricular rhythm relies onconduction of action potentials through the AV node and AV bundle.

Cardiac rhythms that do not follow the normal sequence of eventsdescribed above and/or have rates that are outside a normal range areknown as arrhythmias. Those that result in a heart rate slower thannormal are known as bradyarrhythmias; those that result in a fasterheart rate than normal are called tachyarrhythmias. Tachyarrhythmias arefurther classified as supraventricular tachyarrhythmias (SVTs) andventricular tachyarrhythmias (VTs). SVTs are generally characterized byabnormal rhythms that may arise in the atria or the atrioventricularnode (AV node). Additionally, there are various types of different SVTsand various types of VTs that can be characterized. The most common SVTsare typically atrial flutter (AFL) and atrial fibrillation (AF). Inaddition, many SVTs involve the AV node, for example, AV nodal reentranttachycardia (AVNRT) where the reentrant loop or circuit includes the AVnode. Another type of SVT is an AV reentrant tachycardia (AVRT), wherean AV reentrant circuit typically involves the AV node and an aberrantconducting bundle known as an accessory pathway that connects aventricle to an atrium.

Atrial flutter (AFL) can result when an early beat triggers a “circuscircular current” that travels in regular cycles around the atrium,pushing the atrial rate up to approximately 221 bpm to approximately 320bpm. The atrioventricular node between the atria and ventricles willoften block one of every two beats, keeping the ventricular rate atabout 125 bpm to about 175 bpm. This is the pulse rate that will befelt, even though the atria are beating more rapidly. At this pace, theventricles will usually continue to pump blood relatively effectivelyfor many hours or even days. A patient with underlying heart disease,however, may experience chest pain, faintness, or even HF as a result ofthe continuing increased stress on the heart muscle. In someindividuals, the ventricular rate may also be slower if there isincreased block of impulses in the AV node, or faster if there is littleor no block.

If the cardiac impulse fails to follow a regular circuit in the atriumand divides along multiple pathways, a chaos of uncoordinated beatsresults, producing AF. AF commonly occurs when the atrium is enlarged(usually because of heart disease). In addition, it can occur in theabsence of any apparent heart disease. In AF, the atrial rate canincrease to more than 320 bpm and cause the atria to fail to pump bloodeffectively. Under such circumstances, the ventricular beat may alsobecome haphazard, producing a rapid irregular pulse. Although AF maycause the heart to lose approximately 20 to 30 percent of its pumpingeffectiveness, the volume of blood pumped by the ventricles usuallyremains within the margin of safety, again because the atrioventricularnode blocks out many of the chaotic beats. Hence, during AF, theventricles may contract at a lesser rate than the atria, for example, ofapproximately 125 bpm to approximately 175 bpm.

Overall, SVTs are not typically immediately life threatening whencompared to ventricular arrhythmias, examples of which are discussedbelow.

Ventricular arrhythmias, which originate in the ventricles, includeventricular tachycardia (VT) and ventricular fibrillation (VF).Ventricular arrhythmias are often associated with rapid and/or chaoticventricular rhythms. For example, sustained VT can lead to VF. Insustained VT, consecutive impulses arise from the ventricles at a rateof about 121 to 180 bpm. Such activity may degenerate further intodisorganized electrical activity known as ventricular fibrillation (VF).In VF, disorganized action potentials can cause the myocardium to quiverrather than contract. Such chaotic quivering can greatly reduce theheart's pumping ability. Indeed, approximately two-thirds of all deathsfrom arrhythmia are caused by VF. A variety of conditions such as, butnot limited to, hypoxia, ischemia, pharmacologic therapy (e.g.,sympathomimetics), and asynchronous pacing may promote onset ofventricular arrhythmia.

It has been common practice for an implantable cardioverterdefibrillator (ICD) to monitor heart rate, or more commonly theventricular rate, of a patient and classify the cardiac condition of thepatient based on this heart rate. For example, a tachyarrhythmia may bedefined as any rate in a range above a designated threshold. This rangeis then divided into ventricular tachycardia and ventricularfibrillation zones. The ventricular tachycardia zone may be furtherdivided into slow ventricular tachycardia and fast ventriculartachycardia zones. However, some implanted devices may include only asingle atrial lead which does not include any electrode implanted in aventricle. Despite this, it would be useful if the ventricular heartrate could be monitored using such a device.

As described above, both SVTs and ventricular arrhythmias may lead toventricular rates in excess of 100 bpm. In other words, ventricularrates of SVTs can overlap with rates of tachycardias of ventricularorigin. These SVTs are often well tolerated and require no intervention.Further, physically active patients can have heart rates during exercisethat overlap with their tachycardia rates. Accordingly, discriminationof VT from SVT, including increased heart rates due to exercise, mayrequire more than just knowledge of a patient's ventricular rate. Inother words, using heart rate as the sole criterion to classify thecardiac condition of a patient is often not sufficient.

In those patients who have an implantable device with only a singleatrial lead and no electrode implanted in a ventricle, it would beuseful to detect arrhythmias and/or perform arrhythmia discrimination,e.g., so that a physician could monitor the patient's cardiovascularcondition, and if appropriate, recommend the implantation of an ICD orpacemaker. More generally, it would be useful if such a device couldobtain useful information that is accessible to the patient and/or thepatient's physician to enable the patient's cardiovascular condition tobe appropriately monitored and treated.

SUMMARY

Certain embodiments of the present invention generally relate tosystems, devices and methods that can be used to monitor and treatcardiovascular disease, and more specifically, can be used to determineheart rate (HR), determine respiration rate (RR) and classify cardiacrhythms based on atrial intracardiac electrogram (IEGM) and atrialpressure (AP) signals.

Certain embodiments of the present invention are directed to a systemthat includes an implantable device including an electrically conductivehousing and a single implantable lead attached to the implantabledevice, and methods for use therewith. The system can also include anon-implantable device configured to communicate with the implantabledevice. The single implantable lead can include a pressure sensorconfigured to be implanted in a patient's left atrium. Additionally, thelead has one or more electrodes, which includes an electrode configuredto be implanted in the patient's right atrium. Using at least one of theelectrode(s), and optionally the electrically conductive housing, anatrial intracardiac electrogram (IEGM) signal is obtained. Additionally,the pressure sensor is used to obtain an atrial pressure (AP) signalindicative of pressure in an atrium, e.g., a left atrial pressure (LAP)signal indicative of pressure in the left atrium. Alternatively, theatrial pressure signal can be indicative of right atrial pressure (RAP).In certain embodiments, more than one lead can be attached to theimplantable device.

The atrial IEGM signal is subject to a spectrum transform to obtain anatrial IEGM frequency spectrum, which can be an atrial IEGM frequencypower spectrum, but is not limited thereto. Similarly, the AP signal issubject to a spectrum transform to obtain an AP frequency spectrum,which can be an AP frequency power spectrum, but is not limited thereto.A first measure of heart rate (HR_(IEGM)) is determined based on one ormore peaks in the atrial IEGM frequency spectrum. Additionally, oralternatively, a second measure of heart rate (HR_(AP)) and/or a measureof respiratory rate (RR_(AP)) is/are determined based on one or morepeaks in the AP frequency spectrum. In accordance with an embodiment, anestimate of the patient's actual heart rate is based on at least one ofthe first and second measures of heart rate, which is available forsaving, uploading and/or displaying, along with the measure ofrespiratory rate (RR_(AP)).

In accordance with an embodiment, one or more peaks is/are identified inthe atrial IEGM frequency spectrum that exceed an IEGM threshold(thresh_(IEGM)) and is/are within a sinus rhythm frequency range(frange_(SR)). The first measure of heart rate (HR_(IEGM)) is determinedbased on such identified peak(s).

Further, one or more peaks is/are identified in the AP frequencyspectrum that is/are within a respiratory rate frequency range(frange_(RR)). A measure of respiratory rate (RR_(AP)) is determinedbased on such peak(s).

Additionally, one or more peaks is/are identified in the AP frequencyspectrum that exceeds an AP threshold (thresh_(AP)) and is/are above aminimum heart rate or within a heart rate frequency range (frange_(HR)).The second measure of heart rate (HR_(AP)) is determined based on suchpeak(s). In certain embodiments, any peak that is determined to be aharmonic of the measure of respiratory rate (RR_(AP)), or is within aspecified range of the measure of respiratory rate (RR_(AP)), is notused to determined the second measure of heart rate (HR_(AP)).

In accordance with specific embodiments, arrhythmias are detected and/orarrhythmia discrimination is performed based on one or more peaks in theatrial IEGM frequency spectrum and one or more peaks in the AP frequencyspectrum. This can include identifying one or more peaks, if any, in theatrial IEGM frequency spectrum that is/are within an atrial fibrillation(AF) frequency range (frange_(AF)) and/or an atrial flutter (AFI)frequency range (frange_(ARI)). This can also include using the firstmeasure of heart rate (HR_(IEGM)) to classify the patient's cardiacrhythm as one of ventricular tachycardia (VT), supraventriculartachycardia (SVT) and sinus rhythm (SR).

This summary is not intended to be a complete description of theinvention. Other features, aspects, objects and advantages of theinvention can be obtained from a review of the specification, thefigures, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B, which can collectively be referred to as FIG. 1,illustrate a high level flow diagram that is used to summarize methodsaccording to various embodiments of the present invention.

FIGS. 2A, 2B, 2C and 2D, which can collectively be referred to as FIG.2, illustrate an exemplary atrial IEGM signal, LAP signal, atrial IEGMfrequency power spectrum, and LAP frequency power spectrum, whichcorrespond to a heart rate of 96 beats per minute, a respiration rate of28 breaths per minute, and which are used to detect sinus rhythm.

FIGS. 3A, 3B, 3C and 3D, which can collectively be referred to as FIG.3, illustrate an exemplary atrial IEGM signal, LAP signal, atrial IEGMfrequency power spectrum, and LAP frequency power spectrum, whichcorrespond to a heart rate of 72 beats per minute, a respiration rate of24 breaths per minute, and which are used to detect atrial fibrillation.

FIGS. 4A, 4B, 4C and 4D, which can collectively be referred to as FIG.4, illustrate an exemplary atrial IEGM signal, LAP signal, atrial IEGMfrequency power spectrum, and LAP frequency power spectrum, whichcorrespond to a heart rate of 64 beats per minute, a respiration rate of20 breaths per minute, and which are used to detect atrial flutter.

FIGS. 5A, 5B, 5C and 5D, which can collectively be referred to as FIG.5, illustrate an exemplary atrial IEGM signal, LAP signal, atrial IEGMfrequency power spectrum, and LAP frequency power spectrum, whichcorrespond to a heart rate of 84 beats per minute, a respiration rate of20 breaths per minute, and which are used to detect sinus rhythm.

FIG. 6 depicts an implantable apparatus suitable for practicing variousembodiments of the invention.

FIG. 7 is a schematic of one embodiment of the electronics locatedwithin the implantable housing of the implantable apparatus illustratedin FIG. 6.

FIG. 8 is a system for treating cardiovascular disease according to anembodiment of the present invention.

FIG. 9 is a block diagram of an external patient advisor/telemetrymodule for use in an embodiment of the present invention.

FIG. 10 shows a flexible lead having an LAP sensor in fluid contact withthe patient's left atrium.

DETAILED DESCRIPTION

The following description is of the best modes presently contemplatedfor practicing various embodiments of the present invention. Thisdescription is not to be taken in a limiting sense but is made merelyfor the purpose of describing the general principles of the invention.The scope of the invention should be ascertained with reference to theclaims. In the description of the invention that follows, like numeralsor reference designators will be used to refer to like parts or elementsthroughout. Also, the left-most digit(s) of a reference numberidentifies the drawing in which the reference number first appears.

Embodiments of the present invention generally relate to systems,devices and methods that can be used to monitor and treat cardiovasculardisease, and more specifically, can be used to determine heart rate(HR), determine respiration rate (RR) and classify cardiac rhythms basedon atrial intracardiac electrogram (IEGM) and atrial pressure (AP)signals. Heart rate (HR), as the term is used herein, refers to apatient's ventricular depolarization rate. By contrast, a patient'satrial depolarization rate will be referred to as the atrial rate. BothHR (i.e., ventricular depolarization rate) and atrial rate are typicallyexpressed in beats per minute. RR is typically expressed in breaths perminute. Both beats per minute and breaths per minute can be representedby the same acronym “bpm”, with the applicable unit determinable basedon context.

Embodiments of the present invention are especially useful with animplantable device to which is attached only a single implantable atriallead that includes as few as one electrode and an AP sensor, but are notlimited thereto. Such an implantable device and lead (which cancollectively be referred to as an implantable system) may be implanted,e.g., in a CHF patient.

Methods according to various embodiments of the present invention willfirst be described with reference to the high level flow diagrams ofFIGS. 1A and 1B, which can be referred to collectively as FIG. 1, andthe graphs of FIGS. 2A-2D, 3A-3D, 4A-4D and 5A-5D. FIGS. 2A-2D, 3A-3D,4A-4D and 5A-5D include graphs illustrating atrial IEGM signals (seeFIGS. 2A, 3A, 4A and 5A), LAP signals (see FIGS. 2B, 3B, 4B and 5B),atrial IEGM frequency power spectrums (see FIGS. 2C, 3C, 4C and 5C), andLAP frequency power spectrums (see FIGS. 2D, 3D, 4D and 5D).

Thereafter, devices and systems according to various embodiments of thepresent invention will be described with reference to FIGS. 6-10. Forexample, as will be described below with reference to FIGS. 6-10,embodiments of the present invention described with reference to FIGS.1-5 can be used with a system that includes an implantable deviceincluding an electrically conductive housing, a single implantable leadattached to the implantable device, and a non-implantable deviceconfigured to communicate with the implantable device. As will bedescribed below with reference to FIG. 6, the single implantable leadcan include a pressure sensor configured to be implanted in a patient'sleft atrium, and one or more electrodes, one of which is configured tobe implanted in the patient's right atrium.

Referring now to FIG. 1A, at steps 102 and 122, an atrial IEGM signaland an LAP signal are obtained, e.g., using an implantable device towhich is attached a single atrial lead. Exemplary atrial IEGM and LAPsignals, which can be obtained at steps 102 and 122, are shown in FIGS.2A and 2B, respectively. More specifically, at step 102, at least twoelectrodes are used to obtain the atrial IEGM, one of which isconfigured as an anode, and one of which is configured as a cathode. Inaccordance with an embodiment where the system includes only a singleatrial lead, at least one of the electrodes used to obtain the atrialIEGM is an electrode of the single lead, wherein the electrode isimplanted in the right atrium. For example, the atrial IEGM can beobtained using an electrode implanted within the right atrium configuredas a cathode, and the electrically conductive housing (often referred toas the “can”, “case” or “case electrode”) of the implantable device (towhich the lead is connected) configured as an anode. Where the singlelead also includes a left atrial electrode (e.g., a left atrial tip orring electrode), the atrial IEGM can alternatively be obtained betweenthe electrode implanted within the right atrium and the electrodeimplanted within the left atrium. Other variations are also possible.For example, the atrial IEGM can be obtained using an electrodeimplanted in the right atrium, or in the inferior or superior venacavea. Preferably, an electrode used to obtain the atrial IEGM is incontact with the atrial septum. The LAP signal is likely obtained usingan LAP pressure sensor located at or near a distal end of the singlelead, with the distal end of the lead being implanted in the leftatrium. Additional details of a single lead including an LAP pressuresensor and one or more electrodes are described below with reference toFIGS. 6-10. Rather than obtaining an LAP signal at step 122 using apressure sensor implanted in the left atrium, an alternative type ofatrial pressure (AP) signal can be obtained. For example, it would alsobe possible that a right atrial pressure (RAP) signal be obtained andused in further steps described below. For the remaining discussion,unless stated otherwise, it will be assumed that the AP signal is an LAPsignal. However, it is within the scope of an embodiment that an RAPsignal be used in place of an LAP signal.

Note that in each of the above exemplary electrode configurations, thereare no electrodes implanted in a ventricle, and thus, the atrial IEGMobtained using such configurations may not include clear-cut R-waves,making it more difficult to detect HR, which is typically detected basedon R-R intervals between consecutive R-waves. Nevertheless, embodimentsof the present invention enable a value for HR to be determined, as willbe described below.

At step 104, the atrial IEGM signal is subject to a spectrum transformto obtain an atrial IEGM frequency spectrum, which is preferably anatrial IEGM frequency power spectrum. Similarly, at step 124, the LAPsignal is subject to a spectrum transform to obtain an LAP frequencyspectrum, which is preferably an atrial IEGM frequency power spectrum.In specific embodiments, steps 104 and 124 are accomplished byperforming a discrete Fourier transform (DFT) on the atrial IEGM and LAPsignals, in which case, the results of the transforms can be referredto, respectively, as DFT_(IEGM) and DFT_(LAP). In accordance withcertain embodiments, the atrial IEGM and LAP signals are preconditionedbefore such a time domain to frequency domain conversion is performed.For example, the LAP signal can be high passed filtered (e.g., using acutoff frequency of about 0.125 Hz) to remove the baseline, and theatrial IEGM signal can be low pass filtered (e.g., using a cutofffrequency of about 40 Hz) to remove noise. Such filtering can beperformed in the analog domain. Alternatively, the filtering can beperformed in the digital domain after the implantable device to whichthe lead is connected converts the atrial IEGM and LAP signals todigital signals using analog-to-digital converters (ADCs). After thefiltering, the digital atrial IEGM and LAP signals can be padded withzeros (0s) in order to optimize the lengths of each signal forperforming a Fourier transform. Thereafter, a DFT is performed on theatrial IEGM and on LAP signals to produce the DFT_(IEGM) and theDFT_(LAP), which are exemplary atrial IEGM and LAP frequency spectrums.A first point of the DFT_(IEGM) and a first point of the DFT_(LAP) isoptionally removed. The power of the atrial IEGM and LAP frequencyspectrums can then determined by squaring the absolute value of thefirst half of the points in the DFT_(IEGM) and the DFT_(LAP). The powerof the atrial IEGM frequency spectrum can also be referred to as theatrial IEGM frequency power spectrum, or simply as pDFT_(IEGM). Thepower of the LAP frequency spectrum can also be referred to as the LAPfrequency power spectrum, or simply as pDFT_(LAP). It is also within thescope of an embodiment of the present invention to not convert theatrial IEGM and LAP frequency spectrums to frequency power spectrums, solong as appropriate thresholds are used in the steps described below.For the following discussion, unless stated otherwise, it will beassumed that atrial IEGM and LAP frequency power spectrums aredetermined at steps 104 and 124. However, it is noted that the termsatrial IEGM and LAP frequency spectrums, as used hereafter, are meant toencompass both power and non-power frequency spectrums. Further, it isnoted that alternative techniques than those described herein fordetermining the atrial IEGM and LAP frequency power spectrums (andnon-power spectrums) are also possible, and within the scope of anembodiment of the present invention.

Preferably (but not necessarily), at steps 106 and 116, the frequenciesof the atrial IEGM frequency power spectrum (pDFT_(IEGM)) and the LAPfrequency power spectrum (pDFT_(LAP)) are converted to beats per minute(bpm). This can be accomplished by multiplying the frequencies by 60,which converts the frequencies from Hz to bpm. For the remainder of thisdescription it will be assumed that steps 106 and 116 are performed.However, for those embodiments where steps 106 and 116 are notperformed, the various thresholds and determinations described belowwill be in beats (or breaths) per second, instead of beats (or breaths)per minute. Exemplary atrial IEGM and LAP frequency power spectrumsignals are shown in FIGS. 2C and 2D, respectively.

At step 108, peaks in the atrial IEGM frequency power spectrum(pDFT_(IEGM)) that exceed a corresponding threshold (thresh_(IEGM)) andexceed a minimum HR frequency are identified. The minimum HR frequencycan be, e.g., 39 bpm, but is not limited thereto. In specificembodiments, the minimum HR frequency can be defined based on the lowerbound of a sinus rhythm (SR) frequency range (frange_(RR)), or based onthe upper bound of an RR frequency range (frange_(RR)). In certainembodiments, the minimum HR frequency is determined experimentally tooptimize sensitivity and/or specificity of HR and/or RR or some bestcase between the two. The thresh_(IEGM) can be a programmedpredetermined value. Alternatively, the thresh_(IEGM) can be determinedas part of (or prior to) step 108 based on the atrial IEGM frequencypower spectrum obtained at step 104. For example, the thresh_(IEGM) canbe determined by computing a mean of the atrial IEGM frequency powerspectrum and adding multiple (e.g., 2) standard deviations to thecomputed mean. Other techniques for determining the thresh_(IEGM) arepossible, and within the scope of an embodiment of the presentinvention. FIG. 2C includes an exemplary dashed horizontal line labeledthresh_(IEGM) and a peak in the atrial IEGM frequency power spectrum(labeled HR_(IEGM) Peak) that exceeds the thresh_(IEGM).

If one or more peaks are identified at step 108, then there is adetermination of whether the first identified peak (i.e., the peakcorresponding to the lowest frequency that exceeds the minimum HRfrequency) is within a sinus rhythm (SR) frequency range (frange_(SR)),as indicated at step 110. An exemplary frange_(SR) is from 40 to 120bpm, but is not limited thereto. If the first peak identified at step108 is not within the frange_(SR), or there is no peak that exceeds thethresh_(IEGM), then it is concluded that HR can not be determined basedon the atrial IEGM, and thus, an HR_(IEGM) (i.e., an HR determinationbased on the atrial IEGM) is indeterminate, as specified at step 114. Ifthe first peak identified at step 108 is within the frange_(SR), thenthe HR_(IEGM) is determined to be equal to, and is saved as, thefrequency corresponding to the first peak identified at step 108, asindicated at step 112. For example, referring to FIG. 2C, the HR_(IEGM)is shown as being approximately 96 bpm.

At step 128 the maximum peak in the LAP frequency power spectrum that iswithin the RR frequency range (frange_(RR)) is identified.Alternatively, at step 128 the first peak in the LAP frequency powerspectrum that is within a frange_(RR) is identified. An exemplaryfrange_(RR) is from 9 to 39 bpm, but is not limited thereto. Asindicated by step 130, the RR is determined to be equal to, and is savedas, a frequency corresponding to the peak identified at step 128. FIG.2D illustrates a maximum peak (labeled RR Peak) in the LAP frequencypower spectrum that is within the frange_(RR). In FIG. 2D, the RR isshown as being approximately 28 bpm. The RR is useful for clinicalanalysis, e.g., to determine whether the patient is experiencingrespiratory problems related to CHF, but is not limited thereto.

At step 132, peak(s) in the LAP frequency power spectrum (pDFT_(LAP))that exceed a corresponding threshold (thresh_(LAP)) and exceed theminimum HR frequency are identified. As mentioned above, the minimum HRfrequency can be, e.g., 39 bpm, but is not limited thereto. As alsomentioned above, in specific embodiments, the minimum HR frequency canbe defined based on the lower bound of the frange_(SR), or based on theupper bound of the frange_(RR). The thresh_(LAP) can be a programmedpredetermined value. Alternatively, the thresh_(LAP) can be determinedas part of (or prior to) step 132 based on the LAP frequency powerspectrum obtained at step 124. For example, the thresh_(LAP) can bedetermined by computing a mean of the LAP frequency power spectrum andadding multiple (e.g., 2) standard deviations to the computed mean.Other techniques for determining the thresh_(LAP) are possible, andwithin the scope of an embodiment of the present invention. FIG. 2Dincludes an exemplary dashed horizontal line labeled thresh_(LAP) and apeak (labeled HR_(LAP) Peak) in the LAP frequency power spectrum thatexceeds the thresh_(LAP).

At step 134, there is an identification of the first peak identified atstep 132 (i.e., the peak identified at step 132 corresponding to thelowest frequency) that is not within a relatively low predeterminednumber of beats (e.g., 3 beats) of the RR, and is not an integermultiple of the RR. As indicated at step 136, the frequencycorresponding to the peak identified at step 134 is determined to beequal to, and is saved as, the HR_(LAP), which is a value of HRdetermined based on the LAP signal. The reason to reject a peak within afew beats (e.g., within 3 beats) of the RR, is that such a peak islikely part of the RR peak. The reason to reject any peak that is aninteger multiple (e.g., 2×, 3×, etc.) of the RR, is that such a peak islikely a harmonic of the RR. In exemplary FIG. 2D, the HR_(LAP), whichis determined based on the peak labeled HR_(LAP) Peak, is approximately96 bpm.

At this point, values for HR_(LAP) and RR have been determined andsaved, and a value for HR_(IEGM) may also have been determined and saved(or there has been a determination that HR_(IEGM) is indeterminate). Incertain embodiments, the method stops here, or begins to repeat at thispoint. Such embodiments can be used to determine values for HR and RR,and to track changes in such values. In other embodiments, the methodincludes some or all of the additional steps described below withreference to FIG. 1B. As mentioned above, the AP signal obtained at step122 need not be an LAP signal. Accordingly, the various references toLAP can more generally be references to AP. For examples, pDFT_(LAP) canmore generally be pDFT_(AP), and HR_(LAP) can more generally be HR_(AP).However, for the remainder of this discussion, unless stated otherwise,it will be assumed that the AP signal is an LAP signal, and thus theterms pDFT_(LAP) and HR_(LAP) will typically be used for consistency.

In certain embodiments, the steps described with reference to FIG. 1Aare performed within an implantable device, and the HR_(LAP) and RRvalues, and potentially the HR_(IEGM) value, are stored within thedevice (e.g., in memory and/or registers) and/or such values arewirelessly transmitted to an external (i.e., nonimplanted) device. Inother embodiments, steps 102 and 122 are performed within an implantabledevice, and data corresponding to the signals obtained at step 102 and122 are wirelessly transmitted to an external device that performs theremaining steps. For another example, the external device can save thesignals obtained at step 102 and 122 so that they can be transferred(e.g., uploaded) to a further external device when a patient visits aphysician or clinician, and the further device can perform the remainingsteps. Such an external device can be, e.g., a patient advisory module(PAM), which can also be referred to as a personal advisory module. Itis also possible that some of the steps are performed by one device(e.g., an implantable device), while other steps are performed by one ormore other device (e.g., one or more non-implanted devices). Othervariations are also possible, and within the scope of the presentinvention.

As will be appreciated from the following discussion of FIG. 1A, thevalues obtained by the steps of FIG. 1A along with additional analysisof the atrial IEGM and LAP frequency power spectrums (pDFT_(IEGM) andpDFT_(LAP)) can be used to classify a cardiac rhythm. For example,arrhythmias can be detected and/or arrhythmia discrimination can beperformed based on one or more peaks in the atrial IEGM power spectrumand one or more peaks in the LAP power spectrum.

Referring now to FIG. 1B, at step 142, peak(s) in the atrial IEGMfrequency power spectrum that is/are within an atrial fibrillation (AF)frequency range (frange_(AF)) or an atrial flutter (AFI) frequency range(frange_(AR)), and exceed a corresponding threshold, is/are identified.The same threshold used at step 108 (i.e, thresh_(IEGM)) can be used atstep 142. Alternatively, a lower threshold, referred to as the AFthreshold (thresh_(AF)), can be used at step 142. The thresh_(AF) can bea programmed predetermined value. Alternatively, the thresh_(AF) can bedetermined as part of (or prior to) step 142 based on the atrial IEGMfrequency power spectrum obtained at step 104. For example, thethresh_(AF) can be determined by computing a mean of the atrial IEGMfrequency power spectrum and making the thresh_(AF) equal to thecomputed mean, or equal to the computed mean plus one standard deviationof the computed mean. For another example, the thresh_(AF) can be equalto one-third (or some other fraction or percentage) of thethresh_(IEGM). Other techniques for determining the thresh_(AF) arepossible, and within the scope of an embodiment of the presentinvention. FIG. 2C includes an exemplary dashed horizontal line labeledthresh_(AF).

An exemplary frange_(AR) is from 221 to 320 bpm, and an exemplaryfrange_(AF) is from 321 bpm -450 bpm. A supraventricular tachyarrhythmia(SVT) frequency range (frange_(SVT)) can also be defined, which is usedto detect SVTs other than AF and AFI. An exemplary frange_(SVT) is from121 to 180 bpm. Additionally, a ventricular tachycardia (VT) frequencyrange (frange_(VT)) can also be defined, e.g., from 181 to 220 bpm. Asmentioned above, an exemplary frange_(SR) is from 40 to 120 bpm.Frequency ranges other than the exemplary ranges listed above canalternatively be used and be within the scope of an embodiment of thepresent invention.

At step 144 there is a determination of whether there are multiple peaksin the atrial IEGM frequency power spectrums (pDFT_(IEGM)) that exceedthe thresh_(IEGM) and are within the frange_(AF). As mentioned above, anexemplary frange_(AF) is from 321 bpm -450 bpm. If the answer to thedetermination at step 144 is yes, then at step 162 there is adetermination of whether at least N of peaks in the atrial IEGMfrequency power spectrums (pDFT_(IEGM)) (that exceed the thresh_(IEGM)and are within the frange_(AF)) is/are not harmonic(s) of the HR. Here,N is a preprogrammed integer that can be equal to 1, 2, or more than 2.When N=1, the algorithm will provide more sensitivity, but lessspecificity. When N=2, the algorithm will provide less sensitivity, butmore specificity. In accordance with an embodiment, the HR_(IEGM) isused at step 162 (when determining whether a peak is a harmonic of theHR), assuming the HR_(IEGM) was not considered indeterminate at steps110 and 114. If the HR_(IEGM) was considered indeterminate, then theHR_(LAP) can be used at step 162, or alternatively, step 162 can beskipped.

Step 162 can be performed by determining whether each peak (in theatrial IEGM frequency power spectrums that exceeds the thresh_(IEGM) andis within the frange_(AF)) is an integer multiple (e.g., 2×, 3×, etc.)of the HR. Step 162 can alternatively be performed by assuming thatpeaks separated from one another by a preprogrammed frequency (e.g., byat least 40 bpm) are harmonics of the HR. If the answer to thedetermination at step 162 is yes (i.e., if at least N of the peaksis/are not a harmonic of the HR), then at step 164 there is adetermination of whether there is a strong secondary peak in the LAPfrequency power spectrum (pDFT_(LAP)) at a frequency approximately twicethe HR_(LAP). In accordance with an embodiment, a strong secondary peakis defined as a peak having an amplitude that is within a predeterminedpercentage (e.g., 70%, or 75%) of the amplitude of the peakcorresponding to the HR_(LAP). If the answer to the determination atstep 164 is no, then the cardiac rhythm is classified as AF, as shown atstep 166, and an indication of the AF classification can be stored alongwith a time stamp and/or data corresponding to one or more of thesignals and/or frequency power spectrums used for the AF classification.If the answer to the determination at step 164 is yes, then there willnot be an AF classification, because such a large secondary peak wouldbe indicative of prominent ventricular and atrial waves in the LAPsignal (or more generally, the AP signal), which is indicative of anon-AF rhythm. The order of steps 162 and 164 can alternatively bereversed. It is also within the scope of an embodiment to remove or skipstep 164 completely.

Alternatively, or additionally, one or more other steps can be performedto confirm or reject an AF classification. For example, an energy ratiocan be determined based on the IEGM frequency power spectrum(pDFT_(IEGM)) and compared to a threshold. If the energy ratio exceedsthe threshold, then an AF classification is confirmed. If the energyratio does not exceed the threshold, then an AF classification isrejected. The energy ratio can be the ratio of the cumulative energy inthe frange_(AF) to the cumulative energy in the frange_(SR). The energyratio can alternatively be the ratio of the cumulative energy in thefrange_(AF) to the cumulative energy in the entire IEGM frequency powerspectrum (pDFT_(IEGM)). In still another embodiment, the energy ratiocan be the ratio of the cumulative energy in the potential AF peaks tothe cumulative energy in the frange_(SR).

If the answer to the determination at step 144 is no, the answer to thedetermination at step 162 is no, or the answer to the determination atstep 164 is yes, then flow proceeds to step 146. At step 146 there is adetermination of whether there is at least one peak in the atrial IEGMfrequency power spectrum (pDFT_(IEGM)) that exceeds the thresh_(IEGM)and is within the frange_(AR). As mentioned above, an exemplaryfrange_(AR) is from 221 to 320 bpm. If the answer to the determinationat step 146 is yes, then at step 172 (which is similar to step 162described above) there is a determination of whether each of the peaksidentified at step 146 is a harmonic of the HR. In accordance with anembodiment, the HR_(IEGM) is used at step 172 (when determining whethera peak is a harmonic of the HR), assuming the HR_(IEGM) was notconsidered indeterminate at steps 110 and 114. If the HR_(IEGM) wasconsidered indeterminate, then the HR_(LAP) can be used at step 172, oralternatively, step 172 can be skipped and flow can go directly to step176. If the answer to the determination at step 172 is no (i.e., if atleast one of the peaks is not an integer multiple of the HR), then thecardiac rhythm is classified as AFI, as shown at step 176, and anindication of the AFI classification can be stored along with a timestamp and/or data corresponding to one or more of the signals and/orfrequency power spectrums used for the AFI classification. Additionally,as indicated at step 178, if there is a an AF or AFI classification atone of steps 166 and 176, then the final HR is determined to be equalto, and is saved as, the HR_(LAP). This is because the LAP signal isconsidered to provide a more accurate estimate of HR than the atrialIEGM signal during AF or AFI. The final HR can also be referred to as anestimate of the patient's actual HR.

If the cardiac rhythm is not classified as AF or AFI at one of steps 166and 176, then there is a determination at step 148 of whether theHR_(IEGM) was considered indeterminate. In accordance with anembodiment, if the answer to the determination at step 148 is no, thenthe final HR is determined to be equal to, and is saved as, theHR_(IEGM), as indicated at step 150. If the answer to the determinationat step 148 is yes, then the final HR is determined to be equal to, andis saved as, the HR_(LAP), as indicated at step 182. More generally, incertain embodiments if there has been an AF or AFI classification, thenthe then the final HR is determined to be equal to, and is saved as, theHR_(LAP). This is because the atrial IEGM is considered to provide amore accurate estimate of HR if the patient is not experiencing AF orAFI. Optionally, if there has been an AF classification, and there aremore than a threshold number of peaks in the LAP frequency powerspectrums (pDFT_(LAP)), then the final HR can be consideredindeterminate. Optionally, if there has been an AFI classification, andthere is more than a threshold amount of energy in the LAP frequencypower spectrums (pDFT_(LAP)) within the frange_(AR), then the final HRcan be considered indeterminate.

In certain embodiments, if the HR_(LAP) and the HR_(IEGM) are within apredetermined number of beats (e.g., 3 beats) of one another, either ofthe two, or the average of the two can be identified as, and saved as,the final HR. In certain embodiments, if the HR_(LAP) and the HR_(IEGM)are not within the predetermined number of beats (e.g., 3 beats) of oneanother, the one that is in a more physiological range (e.g., as set bya clinician) is identified as, and saved as, the final HR. As mentionedabove, the final HR can also be referred to as an estimate of thepatient's actual HR. Alternatively, if the HR_(LAP) and the HR_(IEGM)are not within the predetermined number of beats (e.g., 3 beats) of oneanother, then the final HR can be considered indeterminate.

At step 152 there is a determination of whether the final HR is withinthe frange_(VT). As mentioned above, an exemplary frange_(VT) is from181 to 220 bpm. If the answer to the determination at step 152 is yes,then the cardiac rhythm is classified as VT, as shown at step 154. Ifthe answer to the determination at step 152 is no, then at step 156there is a determination of whether the final HR is within thefrange_(SVT). As mentioned above, an exemplary frange_(SVT) is from 121to 180 bpm. If the answer to the determination at step 156 is no, thenat step 160 the cardiac rhythm is classified as SR. Steps 154, 158and/or 160 can also include saving an indication of the rhythmclassification along with a time stamp and/or data corresponding to oneor more of the signals and/or frequency power spectrums used for therhythm classification.

The steps described above with reference to FIGS. 1A and 1B can becontinually repeated, repeated from time-to-time (e.g., periodically oraperiodically), performed on demand (e.g., in response to a triggeringevent), and the like. The final HR, the RR and the cardiac rhythmclassification can be saved and displayed to a patient, physician and/orclinician, optionally along with one or more of the waveforms obtainedat steps 102 and 122 and/or obtained at steps 104/106 and/or 124/126.

FIGS. 2A, 2B, 2C and 2D illustrate an exemplary atrial IEGM signal, LAPsignal, atrial IEGM frequency power spectrum, and LAP frequency powerspectrum. In FIG. 2D the maximum peak in the pDFT_(LAP) within thefrange_(RR) occurs at 28 breaths per minute, and thus, RR=28 breaths perminute. In FIG. 2C the first peak that exceeds the thresh_(IEGM) iswithin the frange_(SR) and corresponds to a HR of 96 bpm, resulting inHR_(IEGM)=96 bpm. In FIG. 2D the first peak that exceeds thethresh_(LAP) and is above the minimum HR frequency (and is not within afew beats of RR and is not an integer multiple of RR) corresponds to anHR of 96 bpm, resulting in HR_(LAP)=96 bpm. Using the embodimentsdescribed above with reference to FIGS. 1A and 1B, a sinus rhythm wouldbe detected, and the final HR=HR_(IEGM)=96 bpm.

FIGS. 3A, 3B, 3C and 3D illustrate another exemplary atrial IEGM signal,LAP signal, atrial IEGM frequency power spectrum, and LAP frequencypower spectrum. In FIG. 3D the maximum peak in the pDFT_(LAP) within thefrange_(RR) occurs at 24 breaths per minute, and thus, RR=24 breaths perminute. In FIG. 3C the first peak that exceeds the thresh_(IEGM) iswithin the frange_(SR) and corresponds to an HR of 72 bpm, resulting inHR_(IEGM)=72 bpm. In FIG. 3D the first peak that exceeds thethresh_(LAP) and is above the minimum HR frequency (and is not within afew beats of RR and is not an integer multiple of RR) corresponds to anHR of 72 bpm, resulting in HR_(LAP)=72 bpm. Note that in FIG. 3C thereare multiple peaks that exceed the thresh_(IEGM) and are within thefrange_(AF), which are indicative of AF. Using the embodiments describedabove with reference to FIGS. 1A and 1B, AF would be detected, and thefinal HR=HR_(LAP)=72 bpm.

FIGS. 4A, 4B, 4C and 4D illustrate a further exemplary atrial IEGMsignal, LAP signal, atrial IEGM frequency power spectrum, and LAPfrequency power spectrum. In FIG. 4D the maximum peak in the pDFT_(LAP)within the frange_(RR) occurs at 20 breaths per minute, and thus, RR=20breaths per minute. In FIG. 4C there is no peak that exceeds thethresh_(IEGM) and is within the frange_(SR), and thus, HR_(IEGM) isindeterminate. In FIG. 4D the first peak that exceeds the thresh_(LAP)and is above the minimum HR frequency (and is not within a few beats ofRR and is not an integer multiple of RR) corresponds to an HR of 64 bpm,resulting in HR_(LAP)=64 bpm. Note that in FIG. 3C there is a peak (atabout 227 bpm) in the pDFT_(IEGM) that exceeds the thresh_(IEGM) and iswithin the frange_(AR). This peak is indicative of the atrial rate, notthe HR (i.e., not the ventricular depolarization rate). Using theembodiments described above with reference to FIGS. 1A and 1B, AFI wouldbe detected, and the final HR=HR_(LAP)=64 bpm.

FIGS. 5A, 5B, 5C and 5D illustrate still another exemplary atrial IEGMsignal, LAP signal, atrial IEGM frequency power spectrum, and LAPfrequency power spectrum. In FIG. 5D the maximum peak in the pDFT_(LAP)within the frange_(RR) occurs at 20 breaths per minute, and thus, RR=20breaths per minute. In FIG. 5C the first peak that exceeds thethresh_(IEGM) is within the frange_(SR) and corresponds to an HR of 84bpm, resulting in HR_(IEGM)=84 bpm. In FIG. 5D the first peak thatexceeds the thresh_(LAP) and is above the minimum HR frequency (and isnot within a few beats of RR and is not an integer multiple of RR)corresponds to an HR of 84 bpm, resulting in HR_(LAP)=84 bpm. Using theembodiments described above with reference to FIGS. 1A and 1B, a sinusrhythm would be detected, and the final HR=HR_(IEGM)=84 bpm.

Embodiments of the present invention described above can be used tomonitor and treat cardiovascular disease, and more specifically, can beused to determine heart rate (HR), determine respiration rate (RR) andclassify cardiac rhythms based on atrial intracardiac electrogram (IEGM)and left atrial pressure (LAP) signals. Based on the HR, RR and/orrhythm classification, a patient can be instructed to take specificmedications and/or to call or visit a physician. Exemplary devices andsystems that can be used to implement such embodiments are describebelow with reference to FIGS. 6-10.

FIG. 6 shows an apparatus for monitoring and potentially treatingcardiovascular disease, such as CHF, which includes an implantablemodule 605 in accordance with one embodiment of the invention. Theimplantable module 605 (which can also be referred to as an implantablesystem) includes a housing 607 and a flexible lead 610. The module 605can be, e.g., a physiologically optimized dosimeter (POD™), such as theHEARTPOD™ device developed by the St. Jude Medical of St. Paul, Minn.Cardiovascular disease, as used herein, shall be given its ordinarymeaning, and shall also include high blood pressure, diabetes, coronaryartery disease, valvular heart disease, congenital heart disease,arrhythmia, cardiomyopathy, and CHF.

The lead 610 is connectable to the housing 607 through a connector 612(also known as a header) that may be located on the exterior of thehousing. In one embodiment, the housing 607 is outwardly similar to thehousing of an implantable electronic defibrillator and/or pacemakersystem. Defibrillator and pacemaker systems are implanted routinely inmedical patients for the detection and control of tachy- andbradyarrhythmias. The flexible lead 610 is also generally similar toleads used in defibrillator and pacemaker systems, except that a compactsensor package 615 is disposed at or near the distal end 617 of the lead610, the opposite end from the connector 612 on the housing 607. Thesensor package 615 includes a left atrial pressure (LAP) sensor, andoptionally one or more further sensors to measure one or more furtherphysical parameters. Signals from the pressure sensor are monitoredcontinuously or at appropriate intervals. Information is thencommunicated to the patient corresponding to appropriatephysician-prescribed drug therapies. In one embodiment, the informationis the treatment signal. In many cases, the patient may administer thedrug therapies to him or herself without further diagnostic interventionfrom a physician.

The lead 610 includes an indifferent electrode 614 which is implanted inthe right atrium. The lead 610 can also include a left atrial electrode616 (e.g., a left atrial ring or tip electrode) in close proximity tothe sensor package 615. Signals indicative of LAP (as detection usingthe LAP sensor 615) and sensed cardiac electrical activity (e.g., asdetected using electrode 614 and/or 616) is transmitted along the lead610 through the connector 612 and to electronic circuitry within thehousing 607.

The housing 607 includes a signal processor (e.g., 757 in FIG. 7) toprocess the signal received from the sensor package 615 via the lead610. The signal processor can also process the atrial IEGM obtainedusing electrode(s) of the lead 610. In addition, the housing 607 mayinclude a telemetry and/or patient signaling module (e.g., 759 in FIG.7), to either communicate with an external device, or signal thepatient, or both. The elements inside the housing 607 may be configuredin various ways, as described below, to communicate to the patient asignal, such as a treatment signal, indicative of an appropriate therapyor treatment based at least in part on one or more of the measuredphysical parameters.

FIG. 6 also shows that the sensor package or module 615 has distal 668and proximal 670 anchoring mechanisms configured to anchor the sensorpackage 615 within the atrial septum of a patient's heart. Oneembodiment showing the contents of the housing 607 is illustrated inFIG. 7.

The housing 607 can have a shape that is flat and oval. In anotherembodiment, the shape is cylindrical, rectangular, elliptical, orspherical. One of skill in the art will understand that a variety ofother shapes suitable for implantation can also be used. In oneembodiment, the housing is about 20 mm by about 30 mm, about 10 mm byabout 20 mm, or about 5 mm by about 10 mm. In one embodiment, thehousing is about 5 mm thick. In one embodiment, the housing is implantedin the patient near the shoulder. In another embodiment, the housing hasdimensions suitable for containing at least some components forcontrolling, powering and/or communicating with a pacemaker and suitablefor implantation inside of the body, as is well known to those of skillin the art. In another embodiment, the housing includes: an antenna, ora coil; a power source, including but not limited to a battery or acapacitor; a signal processor; a telemetry apparatus; a data memory; ora signaling device. In one embodiment, the apparatus is powered by anexternal power source through inductive, acoustical, or radio frequencycoupling. In one embodiment, power is provided using electromagneticemissions emitted from an electrical coil located outside the body. Inone embodiment, power and data telemetry are provided by the same energysignal. In another embodiment, an electrical coil is implanted insidethe body at a location under the skin near the patient's collarbone. Inanother embodiment, an electrical coil is implanted inside the patient'sbody at other locations. For example, in one embodiment, the coil isimplanted under the skin in the lower abdomen, near the groin. One ofskill in the art will understand that the device can be implanted in avariety of other suitable locations.

As shown in FIG. 7, in one embodiment housing 607 includes a battery753, signal processing and patient signaling modules 757, and atelemetry module 759 with an associated antenna (not shown), which iscoupled to the module 757. The housing 607 can optionally also include acardiac rhythm management (CRM) system, which is configured to providean electrical stimulus, such as a pacing signal and/or a defibrillationshock, to the patient's heart. The signal processing module 757 iscoupled to at least one LAP sensor that provides a signal indicative ofthe fluid pressure within the left atrium of the heart. The signalprocessing module 757 is also coupled to the one or more electrodes ofthe lead 610, as well as to the electrically conductive “can”, therebyenabling the module 757 to obtain an atrial IEGM signal. In accordancewith an embodiment, the signal processing module 757 can perform thevarious steps described above with reference to FIGS. 1A and 1B. Thesignal processing module 757 may also be configured to control distallyimplanted CRM components, or a sensor package or module, as described ingreater detail herein. The signal processing module 757 can includememory and/or registers for storing signals and/or values obtained usingembodiments of the present invention described above.

FIG. 8 shows one embodiment of a system 809 for monitoring andpotentially treating cardiovascular disease. The system 809 includes theimplantable module 605, which was described with reference to FIG. 6,and an external PAM 806, such as that described below with reference toFIG. 9. During system operation, radio frequency (RF) or other types ofsignals are carried by the lead 610 between the LAP sensor package 615located near the distal end 617 of the lead 610, and the housing 607 ofthe implantable module 605. The circuitry inside the housing 607includes an antenna coil (not shown). In this embodiment, signals arecommunicated between the implantable module 605 and an external device,such as a patient advisory module (PAM) 806, via the antenna coil of thehousing 607 and a second external coil (not shown) coupled to theexternal device 806.

As was shown in FIG. 7, the housing 607 contains a battery 753 thatpowers the implantable device 605. In another embodiment, the implanteddevice 605 receives power and programming instructions from an externaldevice 806 via radio frequency (RF) transmission between the externaland internal coils. The external device 806 receives signals indicativeof one or more physiological parameters from the implanted device 605via the coils as well. One advantage of such externally poweredimplantable device 605 is that the patient will not require subsequentsurgery to replace a battery. In one embodiment of the presentinvention, power is required only when the patient or the patient'scaregiver initiates a reading. In other situations, where it is desiredto obtain physiological information continuously, or where it is desiredthat the implanted device 605 also perform functions with higher or morecontinuous power requirements, it is preferable that the housing 607contain one or more batteries. As described below, the housing 607 mayalso contain circuitry to perform additional functions that may bedesirable.

FIG. 9 shows one embodiment of the PAM 806. In one embodiment, the PAM806 includes a hand held computer with added hardware and software.Referring to FIG. 9, a PAM 806 includes a radio frequency telemetrymodule 964 with an associated coil antenna 962, which is coupled to aprocessing unit 966. In one embodiment, the processing unit 966 includesa palm-type computer, or personal digital assistant (PDA), or a tabletcomputer, as is well known to those of skill in the art. In oneembodiment, the PAM 806 powers the implanted module (605 in FIGS. 6 and8) with the telemetry hardware module 964 and coil antenna 962. Inanother embodiment, the PAM 806 receives physiological signals from theimplanted module by wireless telemetry through the patient's skin.

The PAM 806 may include an RF unit 968 and a barometer 912 for measuringthe reference atmospheric pressure. In one embodiment, the RF unit 968and barometer are located within the telemetry module 964, although theycan be integrated with the processing unit 966 as well. The signalprocessing unit can be used to analyze physiologic signals and todetermine physiologic parameters. The PAM 966 may also include datastorage, and a sub-module that contains the physician's instructions tothe patient for therapy and how to alter therapy based on changes inphysiologic parameters. The parameter based physician's instructions aretypically referred to as “the dynamic prescription,” or DynamicRx™ (St.Jude Medical Inc.). The instructions are communicated to the patient viathe signaling module 966, or another module. The PAM 966 is locatedexternally and used by the patient or his direct caregiver. It may bepart of a system integrated with a personal digital assistant, a cellphone, or a personal computer, or as a Stand-Alone device. In oneembodiment, the external PAM comprises an external telemetry device, asignal processing apparatus, and a patient signaling device. In oneembodiment, the PAM is operated to obtain the sensor signal from theimplantable sensor by telemetry through the patient's skin; obtain theatmospheric pressure from the barometer; and adjust the sensor signalindicative of a fluid pressure based at least in part upon theatmospheric pressure obtained by the barometer so that the adjustedsensor signal indicates the fluid pressure within the left atrium of theheart relative to the atmospheric pressure.

In one embodiment, the physiologic signals are analyzed and used todetermine adjustable prescriptive treatment instructions that have beenplaced in the PAM 806 by the patient's personal physician. Communicationof the prescriptive treatment instructions to the patient may appear aswritten or graphic instructions on a display of the PAM 806. Thesetreatment instructions may include what medications to take, dosage ofeach medication, and reminders to take the medications at theappropriate times. In one embodiment, the PAM 806 displays otherphysician-specified instructions, such as “Call M.D.” or “Call 911” ifmonitored values become critical.

A third module of this embodiment is designed for physician use. Thethird module is used to program the dynamic prescription and communicateit or load it into the PAM 806. The third module may also contain storeddata about the patient, including historical records of the physiologicsignals and derived parameters transmitted from the patient implant andsignaling modules. The third module may also communicate with externaldatabases. In one embodiment, the third module is a physician inputdevice, and includes a personal computer, a mobile phone, a tablecomputer, a PDA, or any other such device as is well known to those ofskill in the art.

In one embodiment of the present invention, the first implant module(such as, for example, implantable module 605 of FIG. 6) may alsocontain an implant therapy unit, or ITU. The ITU generates an automatictherapy regimen based upon the programmed dynamic prescription. Thetherapy may include, but is not limited to, a system for releasingbioactive substances from an implanted reservoir, a system forcontrolling electrical pacing of the heart, and controllers forventricular or other types of cardiac assist devices. For example, inone embodiment the sensor package is placed across the intra-atrialseptum and serves as the atrial lead of a multichamber pacemaker. Thephysiologic sensor information is used to adjust pacing therapy suchthat pacing is performed only when needed to prevent worsening heartfailure. One skilled in the art will appreciate that many systems ordevices that control the function of the cardiovascular system may beused in accordance with several embodiments of the current invention.

In one embodiment of the invention, the advisory module 806 isprogrammed to signal the patient when it is time to perform the nextcardiac status measurement and to take the next dose of medication. Itwill be recognized by those skilled in managing CHF patients that thesesignals may help the many patients who have difficulty taking theirmedication on schedule. Although treatment prescriptions may be complex,one embodiment of the current invention simplifies them from thepatient's perspective by providing clear instructions. To assure thatinformation regarding the best treatment is available to physicians,professional cardiology organizations such as the American HeartAssociation and the American College of Cardiology periodically publishupdated guidelines for CHF therapy. These recommendations can serve astemplates for the treating physician to modify individual patienttreatment. In one embodiment, the device routinely uploads data to thephysician or clinic, so that the efficacy of the prescription and theresponse to parameter driven changes in dose can be monitored. Thisenables the physician to optimize the patient's medication dosage andother important treatments without the physician's moment-to-momentintervention.

In various embodiments of the invention, a device and method fordynamically diagnosing and treating cardiovascular illness in a patientare provided. In one embodiment, at least one physiological sensor isused to generate a signal indicative of a physiological parameter. Inanother embodiment, signal processing apparatus operable to generate asignal indicative of an appropriate therapeutic treatment based, atleast in part, upon the signal generated by the physiological sensor, isalso provided. In another embodiment a patient signaling device used tocommunicate the signal indicative of the appropriate therapeutictreatment to the patient is provided as well.

In one embodiment, a device and method for continuously or routinelymonitoring the condition of a patient suffering from chroniccardiovascular disease are provided. As will be described in detailbelow, a system incorporating various embodiments of the inventionmonitors various physiologic parameters, such as the patient's leftatrial pressure. Depending upon the magnitude of or changes in thispressure, for example, the system communicates a signal to the patientindicative of a particular course of therapy appropriate to manage orcorrect, as much as possible, the patient's chronic condition. In someembodiments, physician instructions and automated therapy are provided.

In one embodiment, the physiological sensor generates a signalindicative of a physiological parameter on or in the patient's body. Inone embodiment, the signal processing apparatus generates a signalindicative of an appropriate therapeutic treatment based at least inpart upon the signal generated by the physiological sensor. The patientsignaling device may generate signals indicative of therapeutictreatments or courses of action the patient can take to manage orcorrect, as much as possible, the patient's condition.

In one embodiment, this method includes the steps of implanting one ormore physiological sensors substantially permanently within the patient,operating the physiological sensor to generate a signal indicative of aphysiological parameter, processing this physiological signal togenerate a signal indicative of an appropriate therapeutic treatment,and communicating the appropriate therapeutic treatment to a user. Inone embodiment, the user includes, but is not limited to, the patient, acaregiver, a medical practitioner or a data collection center.

In another embodiment, the system is combined with or incorporated intoa CRM system, with or without physiologic rate control, and with orwithout backup cardioversion/defibrillation therapy capabilities.

In one embodiment, at least one indication of congestive heart failure(CHF) is monitored. Elevated pressure within the left atrium of theheart is the precursor of fluid accumulation in the lungs, which resultsin signs and symptoms of acute CHF. Mean left atrial pressure in healthyindividuals is normally less than or equal to twelve millimeters ofmercury (mm Hg). Patients with CHF that have been medically treated andclinically “well compensated” may generally have mean left atrialpressures in the range from 12 to 20 mm Hg. Drainage of fluid into thepulmonary interstitial spaces can be expected to occur when the leftatrial pressure is above about twenty-five mm Hg, or at somewhat morethan about thirty mm Hg in some patients with chronic CHF. Pulmonaryedema has been found to be very reliably predicted by reference to leftatrial pressures and less well correlated with conditions in any otherchamber of the heart. Thus, the methods and apparatus of severalembodiments of the invention may prove very useful in treating andpreventing pulmonary edema and other adverse conditions associated withCHF. Pressure in the pulmonary veins, pulmonary capillary wedgeposition, and left ventricular end diastolic pressure (LVEDP) aregenerally indicative of left atrial pressure and are commonly used assurrogates of LAP. There are, however, specific conditions, that arewell known to those skilled in the art, including cardiologists andphysiologists, where these surrogates vary substantially from LAP andmay be less predictive of impending heart failure. One example of such acondition is mitral valve stenosis where pulmonary edema developsdespite a normal LVEDP due to a significant pressure gradient across themitral valve. Other surrogate pressures that also, on specific occasion,indicate LAP include, but are not limited to: the pulmonary arterydiastolic (PAD) or algorithms that estimate PAD from the rightventricular waveform, the right ventricular end diastolic, and the rightatrial pressure.

An embodiment of the invention includes a permanently implanted devicedesigned to define the presence of worsening CHF hours to days beforethe onset of symptoms and to provide for early preventative treatmentaccording to the physician's individualized prescription. As such, anembodiment of the invention includes an integrated patient therapeuticsystem that determines therapeutic dosages for an individual patientbased at least in part on internal physiologic signals. In anotherembodiment, the system consists of a small implantable sensor device andan external PAM comprising a personal data assistant (PDA) and atelemetry module. The sensor system may be implanted into the patient'sleft atrial chamber by a transseptal catheterization procedure. Thereare already several thousand physicians in the U.S. and abroad with theexperience and skills required for such device implantation. Theimplantation procedure can be performed on an outpatient basis in ahospital's cardiac catheterization laboratory. The implant mayalternatively be placed at the time of open-heart or minimally invasivevalve or bypass surgery where the surgeon, under direct or laparoscopicvision, positions the device in the left atrium, left atrial appendage,or an adjacent pulmonary vein.

In one embodiment, the sensor system obtains LAP and atrial IEGMsignals. Elevated left atrial pressure is the most accurate predictor ofimpending CHF, often preceding clinical symptoms by hours to days. Otherembodiments of the left atrial pressure waveform may be used to diagnosea number of conditions. The sensor package 615 may also include atemperature sensor to monitor core temperature, which is often depressedin acute CHF, but elevated prior to the development of fever in responseto an infection, making core temperature a useful parameter fordifferentiating between these common conditions with similar symptomswhich require different treatments. The atrial IEGM may be useful indiagnosing arrhythmias and precipitating causes of worsening CHF.

In one embodiment, such as that illustrated in FIG. 10, an implantabledevice is implanted percutaneously in the patient by approaching theleft atrium 1036 through the right atrium 1030, penetrating thepatient's atrial septum 1041 and positioning the sensor package 615 inthe atrial septum 1041, on the septal wall of the left atrium 1036, orinside the patient's left atrium 1036. FIG. 10 shows an embodiment inwhich the sensor package 615 is deployed across the atrial septum 1041.The sensor lead 610 is coupled to a physiological sensor or sensors 615and anchoring apparatus at the lead 610 distal end 617. The anchoringapparatus includes a distal foldable spring anchor 668 that expands indiameter upon release and is located at or near the distal tip of thesensor 615, and a proximal foldable spring anchor 670. The distal andproximal anchors 668, 670 are sufficiently close together that whendeployed the two anchors 668, 670 sandwich the intra-atrial septum 1041between them, thus fixing the sensor/lead system to the septal wall. Theintra-atrial septum 1041 is typically between about 1 and about 10 mmthick. In one embodiment, the anchors 668, 670 are made of a highlyelastic biocompatible metal alloy such as superelastic nitinol. The lead610 may contain a lumen that exits the lead 610 at its proximal end.

In accordance with an embodiment, a stiffening or bending stylet can beinsert in the lumen to aid in passage of the sensor(s) 615 and lead 610.After a transseptal catheterization has been performed, a sheath/dilatorsystem of diameter sufficient to allow passage of the sensor/lead systemis placed from a percutaneous insertion site over a guidewire until thedistal end of a sheath 1067 is in the left atrium 1036. Left atrialposition can be confirmed under fluoroscopy by contrast injection, or bythe pressure waveform obtained when the sheath 1067 is connected to apressure transducer. To aid the procedure, the sheath 1067 may include aproximal hemostasis valve to minimize air entrainment during deviceinsertion. A side port with a stopcock is useful to aspirate anyremaining air and to inject radiographic contrast material.Additionally, later sheath 1067 removal may be facilitated by using a“peel-away” type of sheath. These features of vascular sheaths arecommercially available and well know to those familiar with the art.With the spring anchors 668, 670 folded and forming a system withminimal diameter, the system is loaded into the sheath 1067 and advanceduntil the distal spring 668 just exits the sheath 1067 in the leftatrium 1036 and is thus deployed to its sprung diameter. The sheath 1067is carefully withdrawn without deploying the proximal anchor 670 and thesheath 1067 and sensor/lead system are withdrawn as a unit whilecontrast is injected through the sheath 1067 around the sensor leaduntil contrast is visible in the right atrium 1030. The proximal sheath1067 is further withdrawn, allowing the proximal anchor 670 to spring toits unloaded larger diameter, thus fixing the distal portion of thesensor lead to the septum 1041.

It will also be apparent that, in several embodiments, a similarsensor/lead system can be inserted through an open thoracotomy or aminimally invasive thoracotomy, with the anchoring system fixating thesensor/lead to a location such as the free wall of the left atrium, theleft atrial appendage, or a pulmonary vein, all of which provide accessto pressures indicative of left atrial pressure.

Embodiments of the present invention have been described above with theaid of functional building blocks illustrating the performance ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have often been defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the claimed invention. For example, it would bepossible to combine or separate some of the steps shown in FIGS. 1A and1B. For another example, it is possible to change the boundaries of someof the blocks shown in FIG. 7.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the embodiments ofthe present invention. While the invention has been particularly shownand described with reference to preferred embodiments thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the invention.

1. A method, comprising: (a) obtaining an atrial IEGM signal; (b)obtaining an atrial pressure (AP) signal indicative of pressure in anatrium; (c) subjecting the atrial IEGM signal to a spectrum transform toobtain an atrial IEGM frequency spectrum; (d) subjecting the AP signalto a spectrum transform to obtain an AP frequency spectrum; (e)determining a first measure of heart rate (HR_(IEGM)) based on one ormore peaks in the atrial IEGM frequency spectrum; and (f) determining asecond measure of heart rate (HR_(AP)) and a measure of respiratory rate(RR_(AP)) based on one or more peaks in the AP frequency spectrum. 2.The method of claim 1, wherein step (c) can result in the first measureof heart rate (HR_(IEGM)) being indeterminate, and further comprising:(g) determining an estimate of the patient's actual heart rate based onat least one of the first and second measures of heart rate; and (h)saving, uploading and/or displaying the measure of respiratory rate(RR_(AP)) determined at step (f) and the estimate of the patient's heartrate determined at step (g).
 3. The method of claim 1, wherein step (e)comprises: (e.1) identifying one or more peaks, if any, in the atrialIEGM frequency spectrum that exceed an IEGM threshold (thresh_(IEGM))and is/are within a sinus rhythm frequency range (frange_(SR)); and(e.2) determining the first measure of heart rate (HR_(IEGM)) based onthe one or more peaks in the atrial IEGM frequency spectrum identifiedat step (e.1).
 4. The method of claim 1, wherein step (f) comprises:(f.1) identifying one or more peaks in the AP frequency spectrum thatis/are within a respiratory rate frequency range (frange_(RR)); and(f.2) determining the measure of respiratory rate (RR_(AP)) based on theone or more peaks identified at step (f.1).
 5. The method of claim 4,wherein step (f) also comprises: (f.3) identifying one or more peaks inthe AP frequency spectrum that exceeds an AP threshold (thresh_(AP)) andis/are above a minimum heart rate or within a heart rate frequency range(frange_(HR)); and (f.4) determining the second measure of heart rate(HR_(AP)) based on the one or more peaks identified at step (f.3). 6.The method of claim 5, wherein step (f.4) comprises: (f.4.i) determiningwhether a first peak identified at step (f.3) is within a specifiedrange of the measure of respiratory rate (RR_(AP)) or is a harmonic ofthe measure of respiratory rate (RR_(AP)); (f.4.ii) determining thesecond measure of heart rate (HR_(AP)) based on the first peakidentified at step (f.3), if the first peak identified at step (f.3) isnot within a specified range of the measure of respiratory rate(RR_(AP)) and is not a harmonic of the measure of respiratory rate(RR_(AP)); and (f.4.iii) determining the second measure of heart rate(HR_(AP)) based on a second peak identified at step (f.3), if the firstpeak identified at step (f.3) is within a specified range of the measureof respiratory rate (RR_(AP)) or is a harmonic of the measure ofrespiratory rate (RR_(AP)).
 7. The method of claim 1, furthercomprising: (g) detecting arrhythmias and/or performing arrhythmiadiscrimination based on one or more peaks in the atrial IEGM frequencyspectrum and one or more peaks in the AP frequency spectrum.
 8. Themethod of claim 7, wherein step (g) comprises: (g.1) identifying one ormore peaks, if any, in the atrial IEGM frequency spectrum that is/arewithin an atrial fibrillation (AF) frequency range (frange_(AF)); (g.2)if one or more peaks are identified at step (g.1), then determiningwhether any of the peak(s) identified at step (g.1) is/are a harmonic ofa measure of heart rate; and (g.3) if at least N peak(s) identified atstep (g.1) is/are within the AF frequency range (frange_(AF)) and is/arenot determined to be a harmonic of the measure of heart rate at step(g.2), then determining that the atrial IEGM frequency spectrum isindicative of AF, wherein N is an integer that is equal to or greaterthan
 1. 9. The method of claim 8, wherein step (g) also comprises: (g.4)identifying one or more peaks, if any, in the atrial IEGM frequencyspectrum that is/are within an atrial flutter (AFI) frequency range(frange_(AFI)); (g.5) if one or more peaks are identified at step (g.4),then determining whether any of the peak(s) identified at step (g.4)is/are a harmonic of one of the measures of heart rate; and (g.6) if atleast one peak identified at step (g.4) is within the AFI frequencyrange (frange_(AFI)) and is not determined to be a harmonic of the oneof the measures of heart rate, then determining that the atrial IEGMfrequency spectrum is indicative of AFI.
 10. The method of claim 9,where step (g) includes determining that the AP frequency spectrum isnot indicative of AF if there is a secondary peak in the AP frequencyspectrum that is at least a specified percentage of a dominant peak inthe AP frequency spectrum and the secondary peak corresponds toapproximately twice the second measure of heart rate (HR_(AP)).
 11. Themethod of claim 9, wherein: if at step (g) there is a determination thatthe atrial IEGM frequency spectrum is indicative of either AF or AFI,then determining that an estimate of the patient's actual heart rate isequal to the second measure of heart rate (HR_(AP)); and if at step (g)there is not a determination that the atrial IEGM frequency spectrum isindicative of either AF or AFI, then determining that the estimate ofthe patient's actual heart rate is equal to the first measure of heartrate (HR_(IEGM)).
 12. The method of claim 9, wherein: if at step (g)there is not a determination that the atrial IEGM frequency spectrum isindicative of either AF or AFI, then using the first measure of heartrate (HR_(IEGM)) to classify the patient's cardiac rhythm as one ofventricular tachycardia (VT), supraventricular tachycardia (SVT), andsinus rhythm (SR).
 13. The method of claim 1, wherein: the atrial IEGMfrequency spectrum comprises an atrial IEGM frequency power spectrum;and the AP frequency spectrum comprises an AP frequency power spectrum.14. A system, comprising: an implantable device including anelectrically conductive housing; one or more implantable leadsattachable to the implantable device and individually or collectivelyincluding an implantable pressure sensor and one or more electrodes;circuitry configured to obtain, using at least one of the one or moreelectrodes, and optionally the electrically conductive housing, anatrial intracardiac electrogram (IEGM) signal; circuitry configured toobtain, using the pressure sensor, an atrial pressure (AP) signalindicative of pressure in an atrium; one or more processor configured tosubject the atrial IEGM signal to a spectrum transform to obtain anatrial IEGM frequency spectrum; subject the AP signal to a spectrumtransform to obtain an AP frequency spectrum; determine a first measureof heart rate (HR_(IEGM)) based on one or more peaks in the atrial IEGMfrequency spectrum; and determine a second measure of heart rate(HR_(AP)) and a measure of respiratory rate (RR_(AP)) based on one ormore peaks in the AP frequency spectrum.
 15. The system of claim 14,wherein the first measure of heart rate (HR_(IEGM)) can beindeterminate, and wherein the one or more processor is configured to:determine an estimate of the patient's actual heart rate based on atleast one of the first and second measures of heart rate; and whereinthe estimate of the patient's actual heart rate is saved, uploadedand/or displayed along with the measure of respiratory rate (RR_(AP)).16. The system of claim 14, wherein the one or more processor isconfigured to: identify one or more peaks, if any, in the atrial IEGMfrequency spectrum that exceed an IEGM threshold (thresh_(IEGM)) andis/are within a sinus rhythm frequency range (frange_(SR)); anddetermine the first measure of heart rate (HR_(IEGM)) based on the oneor more identified peaks in the atrial IEGM frequency spectrum thatexceed the thresh_(IEGM) and is/are within the frange_(SR).
 17. Thesystem of claim 14, wherein the one or more processor is configured to:identify one or more peaks in the AP frequency spectrum that is/arewithin a respiratory rate frequency range (frange_(RR)); and determiningthe measure of respiratory rate (RR_(AP)) based on the one or moreidentified peaks within the frange_(RR).
 18. The system of claim 17,wherein the one or more processor is configured to: identify one or morepeaks in the AP frequency spectrum that exceeds an AP threshold(thresh_(AP)) and is/are above a minimum heart rate or within a heartrate frequency range (frange_(HR)); and determine the second measure ofheart rate (HR_(AP)) based on the one or more identified peaks in the APfrequency spectrum that exceed the thresh_(AP) and is/are above theminimum heart rate or within the frange_(HR).
 19. The system of claim14, wherein the one or more processor is configured to: detectarrhythmias and/or perform arrhythmia discrimination based on one ormore peaks in the atrial IEGM frequency spectrum and one or more peaksin the AP frequency spectrum.
 20. The system of claim 14, wherein theone or more implantable leads comprise a single lead including theimplantable pressure sensor and the one or more electrodes.
 21. Amethod, comprising: (a) subjecting an atrial intracardiac electrogram(IEGM) signal to a spectrum transform to obtain an atrial IEGM frequencyspectrum; (b) subjecting an atrial pressure (AP) signal to a spectrumtransform to obtain an AP frequency spectrum; and (c) detectingarrhythmias and/or performing arrhythmia discrimination based on one ormore peaks in the atrial IEGM frequency spectrum and one or more peaksin the AP frequency spectrum.
 22. The method of claim 21, wherein step(c) comprises classifying a patient's rhythm as one of sinus rhythm(SR), atrial fibrillation (AF), atrial flutter (AFI), ventriculartachycardia (VT) and supraventricular tachycardia (SVT) withoutobtaining and analyzing an intracardiac electrogram (IEGM) signal usingan electrode implanted in a ventricle.
 23. The method of claim 21,wherein: the atrial IEGM frequency spectrum comprises an atrial IEGMfrequency power spectrum; and the AP frequency spectrum comprises an APfrequency power spectrum.